This invention relates to cathodes for use in the electroforming of metallic structures.
Electrodeposition techniques have, of course, been known for some time. Typically, a cathode is provided having an exposed conductive surface of a suitable shape to cause deposition of metal in a predetermined pattern. Although various techniques for producing such cathodes have been proposed, for many types of products (e.g., fine metallic filaments used to form wire conductors) difficulties in the electrodeposition techniques generally and in cathodes in particular, have prevented the wide-scale commercial acceptance of electrodeposition. A commercially acceptable cathode should be relatively inexpensive to manufacture, should have a relatively long useful lifetime, and should permit the stripping of the, typically delicate, deposited metallic structures from cathode surface. Of the various previous cathode fabrication techniques, some have permitted relatively inexpensive manufacture of cathodes but have resulted in a cathode that was difficult to use and did not have a long lifetime. Other cathode structures have had a longer lifetime that was gained by a design requiring relatively expensive manufacturing techniques.
The following references are cited as illustrative of previously proposed cathode designs. Emerson U.S. Pat. No. 395,773, Sanders U.S. Pat. No. 541,986, and Sanders U.S. Pat. No. 625,205 each teach, essentially, the use of a metal filament wound around a rotary cylindrical member with adjacent convolutions of the filament separated by an insulating material, the filament defining the surface for deposition of metal. In Forsyth et al U.S. Pat. No. 570,125, an insulating rubber strip is set into a spiral groove formed into a passive metal base, spaced between adjacent rubber convolutions forming the plating surface. A number of patents have taught various permutations of photoresist/etch techniques for producing either cathode patterns or circuits inlaid into a backing material. Exemplary of these techniques are: George U.S. Pat. No. 3,368,945; Knisley U.S. Pat. No. 3,582,476; Backwell U.S. Pat. No. 3,703,450; and Jacobus U.S. Pat. No. 3,833,482. Klemm U.S. Pat. No. 3,891,514 forms a cathode by filling depressions in a base with a conductor and then grinding flat the adjacent conductor and base surfaces, a relatively expensive technique. Finally, various cathode fabrication techniques were taught in Wang U.S. Pat. No. 3,929,610, issued Dec. 30, 1975, owned by the assignee of the present application, and incorporated herein by reference; as well as in references cited in the file history of that patent. The Wang patent dealt with a particular cathode design problem to which the present application is also directed. That is, the fabrication of a cathode suitable for electroforming very fine metallic filaments of indefinite length. While the cathode designs of the Wang patent were relatively successful in meeting the desired cathode criteria even in this particularly difficult electrodeposition problem, according to the present invention it has been discovered that other fabrication techniques that are potentially less expensive also yield good results.
In view of the foregoing discussion, it is a principal object of the present invention to provide a method of cathode fabrication which is relatively inexpensive and which yields a cathode of relatively high quality. It is a more particular object of the present invention to provide a method of cathode fabrication in which the expensive items of the method can be used over and over.